This invention relates to an improved stop-motion device for an automatic doffing apparatus of the general type disclosed in U.S. Pat. Nos. 3,786,621, 3,827,227 and 3,823,538, among others. Such apparatus services a textile spinning frame or like machine having at least one row of bobbin-receiving spindles extending longitudinally thereof. The apparatus includes a bobbin grasper member and a reciprocatorily-movable draw bar member which extend generally parallel to the row of spindles along substantially its entire length. A plurality of articulated linkage mechanisms innerconnect the aforesaid members such that, upon reciprocatory movement of the draw bar member, the bobbin grasper member moves between elevated and lowered positions relative to the spindles for the purpose of transporting bobbins thereto and therefrom.
A particularly critical phase of the operation of a doffing apparatus of the above-described type is that during which the bobbin grasper member raises or "doffs" full bobbins (i.e., ones upon which desired quantities of yarn have been wound) from the spindles of the textile machine serviced by the apparatus, and then transports such full bobbins downwardly to a location adjacent the base of the machine. As the full bobbins are doffed from the spindles, the yarn innerconnections between such packages and the textile machine are supposed to be severed, ruptured or otherwise broken. When this occurs the full bobbins will depend in a uniformly proper and non-obstructive manner from the bobbin grasper member during the latter's downward movement from an elevated and to a lowered position. It sometimes happens, however, that the yarn innerconnection will not be broken between the textile machine and one of the many full bobbins simultaneously doffed from the spindles by the bobbin grasper member. Any full bobbin whose yarn innerconnection remains intact during the thereafter ensuing downward movement of the bobbin grasper member will not depend properly from such member, but rather may and likely will be so canted as to become wedged between the bobbin grasper member and the spindle rail or some other component of the textile machine, thus impeding or completely arresting further downward movement of at least one longitudinal expanse of the bobbin grasper member. Attempted continuation of the bobbin grasper member's downward movement in the face of a motion-impeding blockage of the aforesaid or similar type can cause severe structural damage to the bobbin grasper member and/or to other components of the doffing apparatus or the textile machine serviced by it.
In an effort to guard against such undesirable consequences, it has heretofore been proposed to so program the control circuitry of doffing apparatus of the described type as to require operator participation in that part of the apparatus' operating cycle involving the aforesaid "critical" movement of the bobbin grasper member. This approach necessitates the availability of a machine operator who is sufficiently diligent to carefully look for possible impediments to movement of the bobbin grasper member, and who is sufficiently dexterous to halt operation of the apparatus prior to its incurring structural damage in the event that a blockage or impediment is detected. Such approach is undesirable since it places excessive reliance upon the varying capabilities of different operators, and also since it detracts from the efficiency and otherwise fully automated operation of the doffing apparatus.
It has also heretofore been proposed to provide automatic stop-motion means in association with an automatic doffing apparatus for the purpose of detecting blockage of movement of the bobbin grasper member of such apparatus: see U.S. Pat. No. 3,895,482. In all of the various embodiments of the stop-motion means specifically shown and described in the aforesaid patent, the bobbin grasper member is specially constructed so as to provide separate switch contacts in association with each of the bobbin grasper elements spaced along the length of such member. In view of the fact that there would customarily be more than one hundred bobbin grasper elements spaced along the length of the bobbin grasper member, it will be appreciated that stop-motion means of the aforesaid construction significantly increases the cost of the doffing apparatus and requires, for its successful utilization, reliable operation over an extended period of time of myriad switch-contacts. The patent also suggests the possibility of providing only a single stop-motion detector in association with the bobbin grasper member or its driving mechanism in those cases when such member mounts only one or a small number of bobbin grasper elements. The provision of stop-motion means including only a single detector or switch element is also highly desirable from the viewpoint of both economy and reliability, when as in the present doffing apparatus the bobbin grasper member has a multiplicity of bobbin grasper elements spaced along its length. However, such a stop-motion means must at the same time possess sufficient sensitivity as to reliably and immediately detect a blockage of or impediment to movement of the grasper bar member at any point along its considerable length, prior to the effect of such blockage or impediment being transmitted throughout the length of and causing structural damage to such member and/or of other elongate structural components of the doffing apparatus.